Improve accessibility by moving the aria-label to the input

[joachimesque]

Closes #158

[bglw]

Thanks for jumping in @joachimesque ❤️

I left some comments on #158 with some discussion points — I'd love to base any a11y changes on a solid existing implementation of this search pattern done well.

One extra note specific to this PR: There very intentionally isn't an aria-live attribute on the results area — you can read some great opinions on this written up by Scott O'Hara here: Considering dynamic search results and content. There are more takeaways from this writeup that Pagefind should adopt (i.e. the aria-live attribute specifically for a "no results" outcome) that haven't been explored yet, but a big takeaway is avoiding the live announcements for the results area as a whole

[bglw]

👋 Going to close this out for now but feel free to re-open if there's another cut. The files have moved around a bit so some things would have to be copied.

I am planning to do an a11y pass over this and the new UI module before a 1.0 release, so hopefully some of the important aspects will be covered by then.